The typical heating and cooling plant in a building includes numerous pieces of equipment, the operating conditions of which must be monitored. Because of the serious consequences which may result from equipment malfunction, it has been customary for on-location personnel to be informed of system performance. Accordingly, costs in prior heating and cooling system monitoring apparatuses have been high because personnel were required at the plant site. It would thus be a significant advantage if such personnel could be notified of malfunctions at some remote location. By providing an automatic telephone dialing device that calls and plays a pre-recorded message to remotely located maintenance personnel when a malfunction occurs, the present invention achieves this advantage.
To prevent damage to equipment and loss of heating/cooling control for any considerable length of time, it is important that malfunctions be quickly indicated and identifiable so that the problem can be corrected. In addition, when a malfunction has been corrected, it is desirable to have the monitoring apparatus switch off and reset whatever malfunction alarm is activated so that further surveillance may continue. To achieve these ends, the present invention includes a local alarm coupled to each sensor and a common alarm activatable by any sensor signal. The system includes means for automatically dialing a pre-defined telephone number and conveying a pre-recorded message, when the telephone with said number is taken off-hook, the dialing and message conveying means being responsive to any malfunction from a sensor. The local alarm and common alarm are deactivated and reset automatically when a malfunction is no longer present. Also, to assure that the signal directed from one sensor to the common alarm does not feed back to activate an alarm associated with another sensor--which would adversely affect malfunction identification--a rectifier bridge is interposed between each local alarm and the common alarm to provide isolation.
For ease of repair and maintenance, it is also desirable to have a monitoring apparatus in which alarms can be selectively inhibited as desired.
The present invention is directed to achieving the above-discussed desired advantages and objects.